Despite substantial investment, there are many failed attempts to develop and manufacture a blood substitute and at this time there are no currently approved products for use as blood substitutes in North America or Europe. We propose in this application to take a biomimetic approach to the design of red blood cells (RBC) using a powerful nano-molding technique called PRINT TM (Particle Replication in Non-wetting Templates) developed at the University of North Carolina at Chapel Hill. PRINT TM will be used synthesize shape-specific, colloidally stable, hydrogel particles with dimensions and mechanical properties which resemble red blood cells and that are individually deformable in a manner to allow them to pass through the 3 micron sized sinusoids in the spleen. Previous approaches for the design of synthetic blood have focused on i) fluorocarbon emulsions which can dissolve large amounts of blood gases;ii) PEGylated hemoglobin;and iii) liposomal delivery of hemoglobin. Heretofore, no one has reported direct molding of RBC mimics which have the same evolutionarily designed shapes and deformability or modulus as RBCs. The PRINT TM molding technique allows us to independently design and investigate the key criteria necessary for a true replacement for blood, including: shape control, particle modulus or flexibility, surface chemistry and surface ligands including markers of self, flow characteristics and gas transport characteristics. The molded particles are able to sequester hemoglobin and allosteric effectors as a cargo, preventing the release and circulation of free-hemoglobin, to facilitate life-like oxygen carrying capacity, but have it in a form that isolates it from physical contact with various organs to avoid the documented side effects associated with free hemoglobin and its cross-linked derivatives. In addition, we also propose to conjugate "markers of self" onto these deformable molded RBC mimics to minimize elimination by the reticuloendothelial system (RES). Key goals of the program will be to develop an oxygen carrier that is long circulating and has the classical sigmoidal shape of the oxygen equilibrium curve with a surface to volume ratio associated with a true RBC for optimal oxygen carrying and release capacity as demonstrated by in vitro and in vivo studies. The need to develop safe and effective synthetic blood substitutes is clear. There will be an estimated shortage of as much as 4 million units of donor blood in the United States alone by 2030. In addition, there is increasing risk of disease transmission from current blood supplies including HIV, Hepatitis A virus, B19 parvovirus, Hepatitis C virus, and infectious prion proteins the agents associated with variant Creutzfeldt-Jakob disease, mad cow disease, and scrapie. Military uses of blood supplies are also clear. Especially shelf-stable supplies that don't require blood antigen type matching. Beyond blood supply, there is a significant need for innovative oxygen delivery approaches to treat such conditions as stroke, myocardial infarction, coronary blockage, organ preservation for transplantation, and malignant disease which affect more than 4 million Americans each year.